1. Field of the Invention
This invention relates to wire guides used in diagnostic and interventional medical procedures. More specifically, this invention relates to wire guides used for access to complex distal anatomy for diagnostic and interventional procedures.
2. Related Technology
Wire guides (also known as guide wires) have been used in percutaneous entry procedures for diagnostic X-Ray studies and interventional procedures since about the 1950's when the idea of percutaneous, wire guided entry into the vasculature was conceived. A wire guide is typically inserted percutaneously into a body vessel and advanced within the body vessel to a desired location. A catheter is then positioned over the wire guide, inserted into the body vessel percutaneously, and advanced along the wire guide to a desired location.
In order to negotiate the potentially-winding path of the body vessel and to reduce potential damage to the body vessel walls while the wire guide is being advanced, the wire guide preferably has a relatively flexible tip. Also, to further prevent the wire guide from becoming stuck within the body vessel, the wire guide is preferably rotated while being advanced along the body vessel. For example, the rotating distal tip may naturally migrate forward via contact with the body vessel internal walls and static friction forces generated from the contact. More specifically, the rotating movement of the distal tip may cause the wire guide to “walk out of” a depression or a bend in the body vessel. Therefore, to promote rotation of the distal portion of the wire guide upon rotation of the proximal portion by the medical professional, the wire guide preferably has a generally efficient torque transfer between the proximal portion and the distal portion of the wire guide.
Additionally, to improve the pushability and control of the catheter along the body vessel, the wire guide shaft that the catheter is advanced thereover preferably has a relatively high axial stiffness compared to the flexible tip and has a general resistance to kinking or bending so that the wire guide will not become kinked or bent during use. For example, the wire guide shaft preferably has an axial stiffness that is sufficient to prevent the wire guide from folding over itself and becoming obstructed within the body vessel.
However, current wire guide configurations have a number of disadvantages. A small diameter wire guide made from different materials results in several end to end type joints, or joints with sudden diameter changes or both. As a result, areas or points along the length of the wire guide have potentially-dramatic behavior changes, such as in terms of flexibility, kink resistance and diameter. These points can act as obstructions and interfere with advancement of small, fragile catheters. Furthermore, the end to end joints between nitinol and stainless steel can also result in sudden, localized flex points in the stiffer body portion of the wire guide. Flex points are the points at the ends of the splice cannula with sudden changes in stiffness, where the wire guide may kink or bend much easier than the portions of the wire just proximal and just distal to the splice.
One design used to mitigate effects of the steps and kink points utilizes a cannula positioned over a nitinol core wire for the shaft portion of the wire and includes a coil section that abuts the distal end of the cannula to form a smooth outer diameter wire guide. However, the combination of a nitinol core wire and stainless steel cannula has dramatically reduced torque control and kink resistance as compared to a solid nitinol mandrel and dramatically reduced stiffness and pushability as compared to a solid stainless steel mandrel.
Another design used to mitigate effects of the steps and kink points utilizes a coil over the shaft portion of the wire guide. Butt joints are then made between the various coil sections. However, this design does not effectively transfer torque between the proximal and the distal ends of the wire guide. More specifically, when the operator rotates the proximal portion of the wire guide, the coil rotates independently from the core wire and the rotation is not transmitted to the distal tip of the wire guide.
It is therefore desirous to provide a wire guide that maintains a generally constant diameter and that minimizes flex points along the wire guide, while preserving and improving the shaft torque transmission qualities, kink resistance, and stiffness.